1. Field of the Invention
The present invention relates to a semiconductor Hall element formed in an epitaxial layer of one conductivity type grown on a single crystal silicon substrate of the opposite conductivity type.
2. Description of the Prior Art
In line with a recent tendency to integrate more and more semiconductor devices, several attempts have been made to integrate a Hall element in a single crystal semiconductor body together with other circuit elements. One of these attempts is described in U.S. Pat. No. 3,522,494, according to which a semiconductor Hall element is formed in an epitaxial layer having a high resistivity of one conductivity type grown on a single crystal silicon substrate of the opposite conductivity type. The epitaxial layer contains a region of the opposite conductivity type extending from the surface of the epitaxial layer to the substrate forming a boundary p-n junction which, with the p-n junction at the substrate interface, defines in the epitaxial layer an island constituting a Hall element. In the island, a pair of highly doped current terminal regions of the one conductivity type are disposed opposite each other. A pair of highly doped Hall signal voltage terminals of the one conductivity type are also disposed in the island, so that a line connecting the Hall signal voltage terminals is substantially perpendicular to electric current passing through the highly doped current terminal regions. Such a Hall element structure has disadvantages that electric current passing under and outside of the Hall signal voltage terminals reduces Hall signals and that since minor changes of conditions vary electric current paths, fluctuations of characteristics among different Hall elements are great.
The Hall element disclosed in U.S. Pat. No. 3,823,354 can partly remove these disadvantages. In this element, an island of one conductivity type constituting a Hall element consists of a substantially rectangular main part and a pair of small substantially rectangular protrusions which are contiguous to a pair of sides of the main part, which are opposite to each other. A pair of highly doped current terminal regions of the one conductivity type are disposed opposite to each other in the main part of the island and another pair of highly doped Hall signal voltage terminal regions of the one conductivity type are disposed in the small substantially rectangular protrusions so that a line connecting the Hall signal voltage terminals is substantially perpendicular to an electric current passing through the highly doped current terminal regions. By using this structure, since only a small current passes under and outside of the Hall signal voltage terminals, it is possible to obtain great Hall signals and to reduce fluctuations in characteristics among different Hall elements. However, since the Hall signal voltage terminal regions should have a sufficiently large area so that they have a sufficiently small contact resistance, they are necessarily long in the direction of the Hall current and shortcircuit part of the Hall voltage. Therefore, one cannot obtain as intense a Hall voltage signal as expected. Moreover, by this structure the offset voltage, which is one of the most important factors from the practical point of view, has a tendency to increase and fluctuations in characteristics among different Hall elements are also great.
In general, by measuring a static magnetic field by means of a Hall element a signal to noise ratio is determined principally by a signal to offset voltage ratio, because a so-called noise level is less than one thousandth of that of signals. Consequently, if an offset voltage is great, no highly effective sensitivity can be obtained even for great Hall signal voltages. Moreover, it is found that the offset voltage varies with a number of factors so that its temperature dependence is complicated and its fluctuations among different Hall elements are great. These disadvantages would be removed, if the Hall signal voltage terminals were disposed in separate islands which are connected to the main part of the Hall element through bridges having a small cross section of the one conductivity type. However, this structure has another disadvantage that the bridges increase the electric resistance between the main part of the Hall element and the Hall signal voltage terminals. In case the electric resistance of Hall signal voltage terminals is great, the Hall signal voltage varies considerably with small variations in the electric current passing through the Hall signal voltage terminal. Moreover, since the resistance is changed by a magnetoresistance effect, a great resistance impairs the linear dependence of the Hall signal voltage on the magnetic field intensity, which is one of the most important features of a Hall element. It was known also that, in case a Hall signal voltage is constituted by a difference in the potentials of a pair of Hall signal voltage terminals, an offset voltage is produced by non-homogeneous distribution of electric resistivity in a utilized crystal as well as by a geometrical asymmetry of the Hall signal voltage terminals.
According to experiments of the inventors of this invention, the offset voltage also varies considerably with changes in the current path due to slight apparent variations in resistance or due to variations in contact resistance of Hall signal voltage terminals, if the Hall signal voltage terminal does not exceed the boundary of the main island but only touches the latter.